In general, states of matters are divided into three states, i.e., a solid, a liquefied and a gas. When energy is applied to a solid, the sold becomes a liquefied, and when the energy is further applied to the liquefied, the liquefied becomes a gas. When the higher energy is applied to the gas, there is generated plasma in a fourth state of matter which consists of electrons and ions having electric polarity. In nature, plasma is observed in the form of lightening, an aurora, and an ion layer in the air. In daily life, artificially produced plasma is included in a fluorescent lamp, a mercury lamp and a neon sign.
When a gas with high kinetic energy is collided at ultra high temperature, electrons with negative electric charges are dissociated from atoms or molecules, thereby making the plasma. The plasma means the gaseous state which is divided into the electrons with negative electric charges and the ions with positive electric charges. Plasma has the degree of ionization of the electric charges which is significantly high. Plasma generally contains the negative electric charges and the positive electric charges in about equal numbers, so that the electric charges are distributed in about equal density. Therefore, plasma is almost in an electrically neutral state.
The plasma is classified as high temperature plasma and low temperature plasma. The high temperature plasma has high temperature like an arc. The low temperature plasma has nearly normally room temperature because the energy of the ions is low whereas the energy of the electrons is high. The plasma is generated by applying the electrical methods, such as direct current, super-high frequency and electron beam, and is maintained by using the magnetic field.
A plasma generating technique and plasma practical use considerably vary depending on the pressure condition at which the plasma is generated. Since the plasma is stably generated on the vacuum condition with low pressure, the plasma generated in this manner is used for chemical reaction, deposition and corrosion in a semiconductor device fabrication process and a new material composition process. The plasma generated on the air pressure condition is used for processing a harmful gas to environment or manufacturing a new matter.
A plasma reaction apparatus for using the plasma needs to have the operability to start a reaction promptly, the high durability, and the efficiency on reaction. Upon the plasma reaction, the forms of an electrode and a furnace and the conditions for reaction (for example, a voltage and an additive) are decisive factors for the plasma reaction. Accordingly, a desirable constitution of the plasma reaction apparatus needs to be presented to correspond with the required performance, and a technique of a plasma reaction method needs to be presented for the optimization of the reaction conditions.